VANCE-007 Final Report

DAM HYDRAULIC CAPACITY
ASSESSMENT REPORT
(DRAFT)
SOUTH LAKE DAM
VANCE-007
VANCE COUNTY, NC
PREPARED BY:
HDR Engineering Inc. of the
Carolinas under contract with
WOOD E&I Solutions
2020

EXECUTIVE SUMMARY
A hydraulic capacity analysis was completed for the South Lake Dam in Vance County, North
Carolina. The purpose of the study was to analyze the existing potential of the dam for
overtopping during predetermined specified rainfall events using the North Carolina Dam Safety
defined process and templates. The analyses were completed using the United States Army Corps
of Engineers developed software Hydrologic Engineering Center – Hydrologic Modeling System
(HEC-HMS) in combination with Arc-GIS to develop required input parameters. The rainfall
events included in the analyses consist of 24-hour durations with return periods of 25 years, 50
years, 100 years, 200 years, 500 years and 1000 years. Results of the analyses indicate that this
structure is not hydraulically adequate for 25 years, 50 years, 100 years, 200 years, 500 years,
and 1000 years rainfall events. Data, input parameters, and final results can be found on the
attached summary sheets and in the appendices of this report as well as in the associated
electronic file in which all program files are stored.
Drainage Area (Sq. Mi.)=
Curve Number =
Lag Time (min.)=
Rainfall Distribution Methods =
1188.1
928.6
968.9
1010.4
1053.1
1096.9
1141.9
372.8
373.3
373.8
374.3
374.8
ELEVATION
370.3
370.8
371.3
371.8
372.3
58.8
70.1
82.1
STORAGE (ACRE-FT)
0.0
5.8
12.9
20.8
29.3
38.4
48.3
354.3
351.3
351.8
352.3
352.8
353.3
353.8
349.8
NA
ELEVATION
349.8
350.3
350.8
STORAGE (ACRE-FT)
814.4
851.3
889.4
71.27
103
SCS Type 2
SPILLWAY
Primary
Auxiliary
TYPE
Concrete Weir
NA
ELEVATION
24 HOUR - 100 YEAR EVENT, 7.39 INCHES, ELEVATION 351.9 (1.9 FT OVER-TOPPED)
24 HOUR - 50 YEAR EVENT, 6.63 INCHES, ELEVATION 351.7 (1.7 FT OVER-TOPPED)
24 HOUR - 25 YEAR EVENT, 5.89 INCHES, ELEVATION 351.5 (1.5 FT OVER-TOPPED)
TOP OF DAM ELEVATION = 350
SUMMARY OF INPUT PARAMETERS
2.42
SUMMARY SHEET OF HYDRAULIC CAPACITY RESULTS
SOUTH LAKE DAM, VANCE-007
ANALYSIS PERFORMED BY: S. MURPHY, HDR
24 HOUR - 1000 YEAR EVENT, 10.1 INCHES, ELEVATION 352.6 (2.6 FT OVER-TOPPED)
24 HOUR - 500 YEAR EVENT, 9.26 INCHES, ELEVATION 352.4 (2.4 FT OVER-TOPPED)
24 HOUR - 200 YEAR EVENT, 8.18 INCHES, ELEVATION 352.1 (2.1 FT OVER-TOPPED)
VANCE-007SOUTH LAKE DAM OCTOBER 27, 2020
3189.3
NOT TO SCALE
2689.4
2768.6
2849.7
2932.4
3016.5
3102.1
2242.8
2314.1
2386.6
2460.3
2535.3
2611.7
1843.0
1905.8
1970.4
2036.6
2104.1
2172.8
1492.5
1547.9
1604.5
1662.3
1721.4
1781.6
1235.5
1284.2
1334.2
1385.6
1438.4
387.8
388.3
388.8
389.3
389.8
384.8
385.3
385.8
386.3
386.8
387.3
381.8
382.3
382.8
383.3
383.8
384.3
378.8
379.3
379.8
380.3
380.8
381.3
375.8
376.3
376.8
377.3
377.8
378.3
375.3
677.6
710.2
743.9
778.5
501.0
528.4
556.6
585.6
615.3
646.0
353.4
376.0
399.4
423.6
448.6
474.4
232.5
251.0
270.1
289.9
310.3
331.5
135.5
150.3
165.6
181.4
197.8
214.8
94.7
107.8
121.4
369.3
369.8
366.3
366.8
367.3
367.8
368.3
368.8
363.3
363.8
364.3
364.8
365.3
365.8
360.3
360.8
361.3
361.8
362.3
362.8
357.3
357.8
358.3
358.8
359.3
359.8
354.8
355.3
355.8
356.3
356.8
VANCE-007SOUTH LAKE DAM OCTOBER 27, 2020

APPENDIX A
Watershed Boundary

Sources: Esri, HERE, Garmin, USGS, Intermap, INCREMENT P,NRCan, Esri Japan, METI, Esri China (Hong Kong), Esri Korea,Esri (Thailand), NGCC, (c) OpenStreetMap contributors, and theGIS User Community
South Lake Dam - VANCE-007 - Watershed Boundary
Legend
Longest FlowPath
Watershed Bound ary
0 0.75 1.50.375 Miles
Date: 10 /5/2020
/Drainage Area: 2.42 Square MilesFlowpath Length: 3.5 miles

APPENDIX B

Lag Time Calculation
Dam No:VANCE-007 Date:10/26/2020
Dam Name:South Lake Dam Engineer:K. Trefzger
Maximum Potential Retention (inches):S =(1000/cn')-10
Time of Concentration (hours):Tc =l0.8*(S+1)0.7
1140*Y0.5
Basin Data:Input Values in yellow
Curve Number CN =71.2746 from NRCS CN Calculation
S =4.03024 in.
Mean Basin Slope Y =6.03902 %from Watershed Mean slope
Longest Flowpath:3.51 mi.from Watershed Longest flowpath
Flow Length l =18532.8 ft.
Time of Concentration Tc =2.87 Hours Tc =172 mins
Lag Time TL =1.72 Hours TL =103 mins

APPENDIX C
NRCS Curve Number Summary Sheet

Change CN according to TR-55 (see tables below)
NLCD (2016) Landuse TR-55 Landuse HSG A (sq. ft.)CN HSG B (sq. ft.)CN HSG C (sq. ft.)CN HSG D (sq. ft.)CN
Open Water Not Available 66932 100 6693207 63515 100 6351493 122486 100 12248574 958068 100 95806801
Developed, Open Space Open space - Fair condition (grass cover 50% to 75%)648675 49 31785060 877581 69 60553104 5670088 79 447936980 157394 84 13221122
Developed, Low Intensity Residential districts by average lot size: 1/3 acre 504833 57 28775465 433869 72 31238540 2996197 81 242691931 69634 86 5988497
Developed, Medium Intensity Residential districts by average lot size: 1/8 acre 95583 77 7359916 103044 85 8758767 882933 90 79463927 39492 92 3633309
Developed, High Intensity Urban districts - Commercial and business 29567 89 2631461 1609 92 148065 48572 94 4565803 0 95 0
Barren Land Newly graded areas 0 77 0 0 86 0 0 91 0 0 94 0
Deciduous Forest Woods - Fair 2943839 36 105978197 1695640 60 101738392 4500052 73 328503826 2627817 79 207597532
Evergreen Forest Woods - Fair 1011246 36 36404841 1552704 60 93162232 6816322 73 497591507 330449 79 26105456
Mixed Forest Woods - Fair 3039322 36 109415606 2396702 60 143802109 8661314 73 632275896 1870238 79 147748779
Shrub/Scrub Brush - Fair 4510 35 157848 0 56 0 41902 70 2933115 0 77 0
Herbaceuous Herbaceuous - Fair 215404 60 12924230 155139 71 11014875 1282039 81 103845127 326043 89 29017797
Hay/Pasture Pasture - Fair 305788 49 14983617 670235 69 46246191 10862465 79 858134713 283365 84 23802692
Cultivated Crops Row crops (SR + CR) - Poor 0 71 0 0 80 0 1738576 87 151256083 19928 90 1793521
Woody Wetlands Not Available 2198 80 175814 95651 85 8130310 0 90 0 260607 95 24757633
Emergent Herbaceuous Wetlands Not Available 0 80 0 0 85 0 0 90 0 9688 95 920360 Weighted CN=71.27
NOTE: Curve Numbers are from SCS TR-55 with the exception of assumed HSG A (CN=60) for Herbaceous,Open Water, Woody Wetlands, and Emergent Herbaceous
Wetlands.
NOTE: double-check all the land types are being calculated and texts are accurate
NOTE: double-check the exported attribute table has the same table format as the "Export_Output" table

APPENDIX D
Hyetograph Results Used for Analysis

0.0
2.0
4.0
6.0
8.0
10.0
12.0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Cumulative Depth (in)Time (hrs)
Hyetographs for 24-Hour SCS Type II Rainfall Distributions
25YR
50YR
100YR
200YR
500YR
1000YR

APPENDIX E
NOAA Atlas 14 Rainfall Table

Point precipitation frequency estimates (inches)
NOAA Atlas 14 Volume 2 Version 3
Data type: Precipitation depth
Time series type: Partial duration
Project area: Ohio River Basin
Location name (ESRI Maps): Henderson, North Carolina USA
Station Name: -
Latitude: 36.262317°
Longitude: -78.421733°
Elevation (USGS): 446.18 ft
PRECIPITATION FREQUENCY ESTIMATES
by
duration
for ARI
(years):1 2 5 10 25 50 100 200 500 1000
5-min:0.394 0.458 0.522 0.589 0.656 0.709 0.757 0.799 0.846 0.888
10-min:0.629 0.733 0.835 0.942 1.05 1.13 1.2 1.27 1.34 1.4
15-min:0.787 0.921 1.06 1.19 1.32 1.43 1.52 1.6 1.68 1.76
30-min:1.08 1.27 1.5 1.73 1.96 2.15 2.33 2.49 2.68 2.84
60-min:1.35 1.6 1.93 2.25 2.61 2.92 3.21 3.49 3.85 4.15
2-hr:1.58 1.87 2.28 2.69 3.17 3.6 4.01 4.43 4.98 5.46
3-hr:1.67 1.99 2.43 2.88 3.43 3.92 4.4 4.9 5.56 6.17
6-hr:2.01 2.39 2.92 3.48 4.16 4.78 5.4 6.05 6.93 7.75
12-hr:2.38 2.83 3.48 4.16 5.01 5.81 6.61 7.47 8.66 9.78
24-hr:2.83 3.42 4.28 4.96 5.89 6.63 7.39 8.18 9.26 10.1
2-day:3.29 3.96 4.91 5.66 6.66 7.45 8.26 9.09 10.2 11.1
3-day:3.48 4.18 5.17 5.95 7 7.84 8.69 9.56 10.8 11.7
4-day:3.67 4.41 5.43 6.24 7.34 8.22 9.11 10 11.3 12.3
7-day:4.27 5.09 6.2 7.08 8.28 9.23 10.2 11.2 12.6 13.7
10-day:4.84 5.76 6.94 7.86 9.12 10.1 11.1 12.1 13.5 14.6
20-day:6.51 7.69 9.11 10.2 11.8 13 14.2 15.5 17.2 18.5
30-day:8.06 9.49 11 12.2 13.8 15.1 16.3 17.5 19.1 20.3
45-day:10.2 12 13.7 15.1 16.9 18.3 19.6 20.9 22.7 24
60-day:12.3 14.3 16.2 17.7 19.5 20.9 22.3 23.6 25.2 26.5
Date/time (GMT): Mon Oct 26 19:48:32 2020
pyRunTime: 0.0305030345917

APPENDIX F
Outlet Works Rating Curves

Total outlet discharge from the spillway system
Client:NCEM Date:10/26/2020
Project:Overtopping Study Engineer:T.Carter
Dam:South Lake Dam Dam No.VANCE-007
Reservior Water
Level (RWS)
Elevation (ft)
Primary spillway
discharge (cfs)
Total discharge from the
spillway system (cfs)
349.8 0.0 0.0
350.3 126.0 126.0
350.8 356.5 356.5
351.3 654.9 654.9
351.8 1008.3 1008.3
352.3 1409.2 1409.2
352.8 1852.4 1852.4
353.3 2334.3 2334.3
353.8 2852.0 2852.0
354.3 3403.1 3403.1
354.8 3985.8 3985.8
355.3 4598.4 4598.4
355.8 5239.5 5239.5
356.3 5907.9 5907.9
356.8 6602.5 6602.5
357.3 7322.4 7322.4
357.8 8066.7 8066.7
358.3 8834.6 8834.6
358.8 9625.5 9625.5
359.3 10438.7 10438.7
359.8 11273.5 11273.5
360.3 12129.5 12129.5
360.8 13006.1 13006.1
361.3 13902.9 13902.9
361.8 14819.4 14819.4
362.3 15755.2 15755.2
362.8 16709.9 16709.9
363.3 17683.2 17683.2
363.8 18674.6 18674.6
364.3 19683.9 19683.9
364.8 20710.8 20710.8
365.3 21754.9 21754.9
365.8 22816.0 22816.0
366.3 23893.8 23893.8
366.8 24988.1 24988.1
367.3 26098.6 26098.6
367.8 27225.0 27225.0
368.3 28367.2 28367.2
368.8 29525.0 29525.0
369.3 30698.1 30698.1
369.8 31886.3 31886.3
370.3 33089.5 33089.5
370.8 34307.5 34307.5
371.3 35540.0 35540.0
371.8 36786.9 36786.9
0.0
5000.0
10000.0
15000.0
20000.0
25000.0
30000.0
35000.0
40000.0
345.0 350.0 355.0 360.0 365.0 370.0 375.0Total discharge from the spillway system (cfs)Reservior Water Level (RWS) Elevation (ft)
The whole spillway system rating curve (cfs)